This invention relates generally to an additive and a method for improving the efficiency of hydraulic fracturing operations conducted in subterranean formations penetrated by a wellbore. It often becomes necessary or desirable to exploit modern technology to increase the rate of fluid flow in wellbores for the production of oil or gas. A common technique for increasing the rate of fluid flow comprises fracturing the subterranean formation adjacent to the wellbore by pumping a fracturing fluid into the wellbore at a pressure sufficient to lift the overburden and fracture the formation. Proppants in the form of uniform size sand, resin coated sand or glass beads are pumped with the fracturing fluid and fill the fracture with porous material to prevent reclosure once hydraulic pressure is released.
In hydraulic fracturing operations, it is important that the fracturing fluid not penetrate into the formation, since the penetration would limit the efficiency of the fracturing process and damage the formation. Penetration of the fracturing fluid typically is controlled by incorporating a fluid loss control additive in the fracturing media.
A variety of different fluid loss control additives are known and used. These include finely divided inorganics such as silica flour, crushed limestone, rocksalt, talc, kaolin and bentonite. These materials are generally insoluble in aqueous hydraulic fluids and tend to plate out and plug the face of the subterranean formation to form an effective filter cake, however, since these materials are inert, they can permanently plug the formation pore spaces, thereby reducing the flow of fluids into the wellbore. Also, many known fluid control additives have poor "spurt loss" characteristics because the filter cake produced by the additive is too slow to form.
Another class of materials used to control fluid loss are natural and modified polysaccharides such as starch, guar, modified guar and xanthan gums, sometimes combined with pulverulent inorganic solids to achieve more desirable properties. Starches are readily degraded to soluble products after completion of the fracturing process, thereby eliminating the plugging problem. Degradation is accomplished by oxidation, enzymatic hydrolysis or the action of bacteria present in boreholes.